Strange HP-31E Function
10-16-2016, 01:35 AM
Post: #1
 aj04062 Member Posts: 156 Joined: Dec 2013
Strange HP-31E Function
I am not sure how to describe this, but I have a 31E that works like a currency adder. In other words:
enter 999
and the calculator interprets this as 9.99
no matter what I enter, the decimal is fixed one place from the left.

However, if I multiply the value, the decimal place will shift to the right and the commas appear where they are supposed to.

If I enter a value using scientific notation, the calculator displays the decimal correctly (when in Fixed mode)

It passes the self test.

My other 31E does not function like this.

Ideas?
10-16-2016, 03:52 AM
Post: #2
 Katie Wasserman Super Moderator Posts: 629 Joined: Dec 2013
RE: Strange HP-31E Function
(10-16-2016 01:35 AM)aj04062 Wrote:  Ideas?

Does it pass the self test?
I had a wacky 38e that did something similarly weird and it failed the self test.

-katie

10-16-2016, 10:26 AM
Post: #3
 PANAMATIK Senior Member Posts: 938 Joined: Oct 2014
RE: Strange HP-31E Function
(10-16-2016 01:35 AM)aj04062 Wrote:  Ideas?

This is very likely a ROM bit error, which can result in strange unpredictible behaviour. I own a HP-25C, which couldn't calculate trigonometric functions correctly until I discovered a single errouneous bit in one of its ROM chips.

Bernhard

That's one small step for a man - one giant leap for mankind.
10-16-2016, 02:55 PM
Post: #4
 Katie Wasserman Super Moderator Posts: 629 Joined: Dec 2013
RE: Strange HP-31E Function
(10-16-2016 10:26 AM)PANAMATIK Wrote:
(10-16-2016 01:35 AM)aj04062 Wrote:  Ideas?

This is very likely a ROM bit error, which can result in strange unpredictible behaviour. I own a HP-25C, which couldn't calculate trigonometric functions correctly until I discovered a single errouneous bit in one of its ROM chips.

Bernhard

I agree and I'm pretty sure that the Spice self test does a checksum of the ROM, so it should fail on AJ's 31E.

-katie

10-16-2016, 05:15 PM
Post: #5
 PANAMATIK Senior Member Posts: 938 Joined: Oct 2014
RE: Strange HP-31E Function
(10-16-2016 02:55 PM)Katie Wasserman Wrote:  I agree and I'm pretty sure that the Spice self test does a checksum of the ROM, so it should fail on AJ's 31E.

As the 31E passes the selftest, I'm not longer sure about the ROM bit error theory. Perhaps it is a fault of some register in the arithmetik logic unit. For test purpose and if it is a solderless version, the 40-pin chip can be easily replaced by one from another spice model.

Bernhard

That's one small step for a man - one giant leap for mankind.
10-16-2016, 10:02 PM (This post was last modified: 10-16-2016 10:04 PM by aj04062.)
Post: #6
 aj04062 Member Posts: 156 Joined: Dec 2013
RE: Strange HP-31E Function
A bit more "functionality".

After charging all night (batteries were almost out), it seems to behave a bit more normal. I thought that might be the cure: undercharged battery.

However, it still does it, but now I can force it out if it doesn't start up working correctly (sometimes it is fine). All I did was enter a value with a decimal, clear then re-enter. The second entry displays correctly.

I have some dead 31's. Maybe I swap the chip to see if it is gone for good.
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